1. Field of the Invention
The present invention relates to an antenna device that transmits and receives a high-frequency signal, and a wireless communication terminal.
2. Description of the Related Art
As described in Japanese Unexamined Patent Application Publication No. 2002-325013 and Japanese Unexamined Patent Application Publication No. 2001-156526, there are practically used antenna devices of related art each including an antenna coil configured of a spiral-shaped conductor pattern formed on a front surface of a substrate.
When such an antenna device is connected to an external circuit, in many cases, the antenna device is arranged with closely located terminals that are connected to an inner peripheral end and an outer peripheral end of the antenna coil. Hence, a routing configuration from the inner peripheral end of the antenna coil (an inner peripheral end of the spiral-shaped conductor pattern) to a region outside the spiral shape and a routing configuration from the outer peripheral end of the antenna coil (an outer peripheral end of the spiral-shaped conductor pattern) to a region inside the spiral shape are required.
Referring to Japanese Unexamined Patent Application Publication No. 2002-325013, a spiral-shaped conductor pattern is formed on a first surface of a substrate. A routing conductor is formed on a second surface (a surface opposite to the first surface) of the substrate. An inner peripheral end of the spiral-shaped conductor pattern is connected to the routing conductor by a through-hole conductor penetrating through the substrate. The inner peripheral end of the spiral-shaped conductor pattern is connected to an external circuit pattern having a spiral-shaped conductor pattern through the through-hole conductor and the routing conductor.
Referring to Japanese Unexamined Patent Application Publication No. 2001-156526, a spiral-shaped conductor pattern is formed on a first surface of a substrate, and a routing conductor (a bridge conductor) is formed on the spiral-shaped conductor pattern. In a region where the routing conductor (the bridge conductor) and the spiral-shaped conductor pattern overlap each other, an insulating layer is arranged between the routing conductor and the spiral-shaped conductor pattern. For example, such an insulating layer is formed by applying an insulating paste. The routing conductor is formed by applying a conductive paste on the insulating later.
With the configuration described in Japanese Unexamined Patent Application Publication No. 2002-325013, since the through-hole conductor has to be formed in the substrate, the load of the process may be increased. Also, since the through-hole conductor is formed by plating the through hole, and the spiral-shaped conductor pattern and the routing conductor are formed by patterning the surfaces of the substrate, connection reliability between the through-hole conductor and the spiral-shaped conductor pattern and connection reliability between the through-hole conductor and the routing conductor may not be in good condition. In addition, since the substrate having the conductors formed on both sides has to be used, the degree of selectivity of the substrate may be decreased.
With the configuration described in Japanese Unexamined Patent Application Publication No. 2001-156526, since the routing conductor is formed with the conductive paste, for example, if a silver paste is used, electrochemical migration of the silver may occur and the possibility of occurrence of a short circuit may be increased. Also, since the routing conductor is formed with the conductive paste, the possibility of breakage of the routing conductor may be increased due to a curve or a bend. That is, with the configuration described in Japanese Unexamined Patent Application Publication No. 2001-156526, reliability of the routing conductor may be decreased.